NEXT GENERATION ANODES FOR LI-ION BATTERIES

FUNDAMENTAL STUDIES OF SI-C MODEL SYSTEMS

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ROBERT KOSTECKI2016 U.S. DOE HYDROGEN and FUEL CELLS PROGRAM and VEHICLE TECHNOLOGIES OFFICE ANNUAL MERIT REVIEW AND PEER EVALUATION MEETING

This presentation does not contain any proprietary, confidential, or otherwise restricted information

Project ID:ES262

Next Generation Anodes for Li-ion BatteriesFundamental Studies of Si-C Model Systems

• This presentation describes coordinated research task within the five National Laboratory consortium to develop practical Si-based Li-ion negative electrode. (Ref. ES261)

• The primary objective of this effort is to provide basic understanding and effective mitigation of key R&D barriers to implementation of silicon-based anodes.

• The technical approach involves fundamental diagnostic studies of basic properties of the Si anode active and passive components in model systems.

Timeline Budget Start: October 1, 2015 FY16 Total Funding: $4000K

– Kickoff: January, 2016 End: September 30, 2018

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Jones at al., Experimental Mechanics, 2014, 54, 971

The Silicon-Carbon Composite Electrode

• Si/C composite electrode is a complex multicomponent electrochemical systems that incorporate widely dissimilar phases in physical, electrical and ionic contact.

• Basic properties of constituent phases determine the behavior of the composite electrode and the entire Li-ion battery system.

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The Silicon-Carbon Composite Electrode

Credit: Yi Cui, Stanford University

• Si/C composite electrode is a complex multicomponent electrochemical systems that incorporate widely dissimilar phases in physical, electrical and ionic contact.

• Basic properties of constituent phases determine the behavior of the composite electrode and the entire Li-ion battery system.

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Abarbanel et al., J. Electrochem. Soc. 2016,163, A522

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The Silicon-Carbon Composite Electrode

•! Si/C composite electrode is a complex multicomponent electrochemical systems that incorporate widely dissimilar phases in physical, electrical and ionic contact.

•! Basic properties of constituent phases determine the behavior of the composite electrode and the entire Li-ion battery system.

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Diagnostic Evaluation of Si-C AnodesChallenges

1. Inherent non-passivating behavior of Si in organic electrolytes

• Large irreversible capacity loss

• Gradual electrolyte consumption and lithium inventory shift in Si-based cells

2. Large volume changes of Si (320%) during cycling

• Cracking and decrepitation of Si

• Loss of electronic connectivity and mechanical integrity

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Characterization Strategies for Si/C Anodes

•! Design unique experimental methodologies for characterization of model Si, C and Si-C electrodes in a single particle, thin-film and monocrystal configurations.

•! Apply ex situ and in situ optical and X-ray probes capable of sensing surface layers at a submonolayer sensitivity and resolution.

Function and Operation of Multipurpose Binders in Si/C Anodes

•! Electrochemical performance of Si/C electrodes varies strongly with different binders. •! The rate and mechanism of the electrode degradation may depend on the binder properties.

Thorough understanding of the binder modes of operation cannot be gained solely through testing commercial-type devices.

•! Electronically and/or ionically conductive •! Chemically stable •! Good mechanical properties •! Compatible with electrode/cell manufacturing

processes

Liu et al., Adv. Mater. 2011, 23, 4679

PPY LiO O

n PAALi

15% Si, 73% graphite, 12% binder, 3 mg/cm2 composite anode

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Function and Operation of Binder(s) in Si/C Anodes

1. Spin-coat PPALi, PVdF, PPy on Cu, p-Si wafer, glassy carbon substrates.

2. Carry out electrochemical measurements of model thin-film electrodes in baseline electrolyte(s).

3. Probe ex situ binder films after electrochemical tests (CVs, galvanostatic cyling etc)

4. Conduct ex situ and in situ studies of selected binder thin film electrodes to probe and monitor their phys-chem parameters.

5. Evaluate binders in tested composite Si-C electrodes.

15-20 nm

Substrate

Model electrodes preparation and testing

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Si(100)/PPy electrode

0.2 mV/s

Characterization of Si/Binder Model ElectrodesProbing Interfacial Properties of Binders

Si/PPy 2:1 composite electrode

0.02 mV/s

1.2 M LiPF6, EC:DEC (3:7) + 30 % FEC 1.2 M LiPF6, EC:DEC (3:7) + 30 % FEC

750 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250

840carboxy group

1300

Abso

rban

ce (-

)

Wavenumbers (cm-1)

pristine cycled electrolyte

1730pyrene

• Preliminary tests show that the model electrodes exhibit more side reactions than the baseline Si/C anodes.

• Electrochemical response varies strongly with different Si-binder arrangements.

• Origins of these interfacial phenomena will be the focus of future studies: Standard electrochemical measurements. Probing ionic and electronic conductivity of binders. Advanced spectroscopy and microscopy of C/binder

and Si/binder interfaces and interphases.

O O

nPPy

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Function and Operation of Binder(s) in Si/C AnodesTesting mechanical properties of binders before and after

electrochemical cycling• Stress-strain curves for binder thin films.• Indentation measurements• Adhesion tests• Morphology changes.

How mechanical properties of the binder help withstand large volumetric changes in Si/C composites and assure composite electrode’s mechanical integrity?

a-Si

c-Si

Vogl et al, Langmuir, 2014,30,10299

10 µL dispersion of polymer in NMP between two Si wafer pieces (1 x 1 cm). Adhesion measurements performed at 1 in/min rate.

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Solid Electrolyte Interphase at Si/C Anodes

http://webb.cm.utexas.edu/research/research_SEI.html

Li+e-

SEIPeled et a;., J. Electrochem. Soc., 144(8), L208 (1997)

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TEM Analysis of Discharged Si Particles after Formation

0 1 2 3 4 5 6 7 8 9 10

0

50

100

150

200

250

300

P Kα

Cu LαF Kα

Si Kα

Cu Kα

O Kα

Cou

nts

E/ KeV

C Kα

Si Particle Edge 2(mostly SEI)

SEI

Si Anode in Gen2 +10% FEC Electrolyte

• SEI layer on Si is highly inhomogeneous and it displays poor passivating properties.

• The chemical composition, structure and function of the SEI are not well understood because of:• Fine structure and nonhomogeneous properties

of electrode/electrolyte interphase.• Technical barriers associated with characterization

methodologies.

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In situ EQCM-D Studies of SEI on Model Si Electrodes

Current Mass

Dissipation

SEI formation PVD Si thin-film (100 nm) electrode, Gen-2 electrolyte, v=1mVs-1

•! Goals: (i) evaluate the effect of electrolyte composition, surface composition and morphology on the formation and properties of the SEI, (ii) assess physico-chemical properties of binders.

•! Preliminary measurements during initial cycles indicate gradual changes of the mass and mechanical properties of the surface film.

• SEI in presence of FEC electrolyte is ~4x thinner than in base electrolyte. It consists mostly of LiF.

• SEI thickness in base electrolyte varies greatly with cycling.

EC/DMC

EC/DMC- 5% FEC

In Situ Neutron Scattering (SANS) Studies of the SEI

θ

θ

θ

Q

d

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Diameter: 30-60 nm ; Length ~ 10 µm

110 105 100 95

Si4+

Inte

nsity

(Arb

. Uni

ts)

Binding Energy (eV)

Si 2p - Si nanowires

Sio

540 535 530 525

Inte

nsity

(Arb

. Uni

ts)

Binding Energy (eV)

O1s - Si nanowire

Si-O, C-O

440 460 480 500 520 540 560

Inten

sity,

Arb.

U.

Raman Shift, cm-1440 460 480 500 520 540 560

Raman Shift (cm-1)

Inte

nsity

(Arb

. Uni

ts)

Si nanowires

1.4 µW24.5 µW120 µW200 µW500 µW770 µW1.16 mW2.57 mW

7.03 mW

440 460 480 500 520 540 560

Inten

sity,

Arb.

U.

Raman Shift, cm-1440 460 480 500 520 540 560

Raman Shift (cm-1)

Inte

nsity

(Arb

. Uni

ts)

Si wafer

1.4 µW

120 µW

1.16 mW

7.03 mW

XPS show SiOx surface layer of thickness < 10 nm that can be removed by a simple etching process

Vaddiraju and coworkers, Materials Letters, 100, 106-110, 2013Vaddiraju and coworkers, Chemistry of Materials, 26, 2814, 2014 Peng et al, Angew. Chem.-Int. Edit., 44, 2737-2742, 2005

Si Nanowires Model Electrode for Interfacial Studies

In operando Electrochemical Acoustic Time of Flight (EAToF) on Si-NMC cells (collaboration with Dan Steingart, Princeton University).

Soft X-ray microscopy and nanotomographyof cycled/degraded silicon and silicon-carbon composite electrodes.

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Spectral Individuation of the LiBOB-Induced Passivation Film on Si-111 by Near-Field IR Spectroscopy

•! High lateral and axial resolution of the near-field optical probe enable spectral and chemical selectivity to select out peaks associated with a single compound

•! Matching early-stage near- and far-field IR spectra allows isolation of the passivating oligomer LiB2C10O20, confirms its presence in the “inner SEI”, establishes structure-function relationship

AFM topography

Topography

Si(111) wafer at 1.5 V in 1M LiPF6 + 2 % LiBOB, EC:DMC [1:1] h#

ES085

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Studies of Solid Electrolyte Interphase at Si/C Anodes

Si-wafer

1.! Use photo-lithography to produce micro-patterned Si/C electrode.

2.! Carry out electrochemical tests of model Si/C electrodes in baseline electrolyte(s).

3.! Apply ex situ and in situ optical and X-ray probes capable of sensing surface layers at submicron resolution.

4.! Monitor and analyze local SEI formation on silicon, carbon and Si-C boundaries.

Model Si/C electrodes preparation and testing Si C Si C ..

Probe interfacial properties and evaluate (in)compatibilty of Si and C surface chemistry on the electrochemical performance of Si/C composite electrodes.

SummaryInitiating Extensive Diagnostic Studies of Model Silicon System

1. Formed collaborative multi-National Lab team to study fundamental phenomena that control the performance of Silicon composite electrodes.

2. Established new and unique experimental capabilities to produce Si, Si/binder, Si/C model electrodes. Initiated integrated electrochemical and analytical diagnostic studies on model systems.

3. Preliminary tests of model Si/PPy electrodes show that the PPy binder is electrochemically stable during initial cycles.

4. More fundamental studies is needed to probe, characterize and evaluate interfacial behavior of model Si/C systems vs. electrochemical performance of the composite silicon anode.

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Explore and study range of silicon and silicon-carbon model systems materials to establish correlations between properties of active and passive components and electrochemical performance of Si composite anode. Assess failure modes in Si and Si-based materials and electrodes. Establish general rules of the surface-structure-composition-property

relationships for Si-based materials and electrodes. Develop new and expand existing in situ and ex situ diagnostic approaches:

– Far- and near-field optical micro-spectrometry of electrode/electrolyte interfaces at molecular resolution.

– Advanced EELS to study lithium transport phenomena in bulk particles, across interfaces, and through grain boundaries.

– Surface sensitive techniques such as synchrotron XPS, soft XAS, atom probe tomography (APT) and neutron reflectometry to study the composition of interfacial layers as a function of state-of-charge, electrolyte composition, etc.

– 1H, 2D, 6Li, 7Li, 13C, 19F, 31P Multinuclear Correlation NMR spectroscopy and new in situ MAS NMR techniques

Future Work

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CONTRIBUTORS AND ACKNOWLEDGMENT

Contributors Daniel Abraham Eric Allcorn Chunmei Ban Javier Bareno Ira Bloom Anthony Burrell James Ciszewski Claus Daniel Dennis Dees Fulya Dogan Key Zhijia Du Alison Dunlop Trevor Dzwiniel Kyle Fenton Kevin Gallagher James Gilbert

Jinghua Guo Aude Hubaud Andrew Jansen Christopher Johnson Baris Key Robert Kostecki Gregory Krumdick Jianlin Li Min Ling Gao Liu Wenquan Lu Jagjit Nanda Kaigi Nie Ganesan Nagasubramanian Christopher Orendorff Cameron Peebles Bryant Polzin

Krzysztof Pupek Philip Ross Tomonori Saito Yangping Sheng Seoung-Bum Son Robert Tenent Lydia Terborg Wei Tong Stephen Trask John Vaughey Gabriel Veith David Wood Jing Xu Linghong Zhang Lu Zhang Shuo Zhang Zhengcheng Zhang

Post-Test Facility (PTF) Materials Engineering Research Facility (MERF) Cell Analysis, Modeling, and Prototyping (CAMP)

Battery Manufacturing Facility (BMF) Battery Abuse Testing Laboratory (BATLab)

Research Facilities

Support for this work from the ABR Program, Office of Vehicle Technologies,DOE-EERE, is gratefully acknowledged – Peter Faguy, David Howell

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